Ferroelectric optical image comparator

Abstract

A ferroelectric optical image comparator has a lead lanthanum zirconate titanate thin-film device which is constructed with a semi-transparent or transparent conductive first electrode on one side of the thin film, a conductive metal second electrode on the other side of the thin film, and the second electrode is in contact with a nonconducting substrate. A photoinduced current in the device represents the dot product between a stored image and an image projected onto the first electrode. One-dimensional autocorrelations are performed by measuring this current while displacing the projected image.

What is claimed is: 
     
       1. An image comparator device comprising a thin-film ferroelectric material having a first surface and a second surface, said first surface being coated with a semi-transparent conductive material to form a first electrode, said second surface being coated with a conductive material to form a second electrode, means for supplying a first voltage across said electrodes to polarize all of the ferroelectric domains in said ferroelectric material toward the second electrode, means for supplying a second smaller voltage of opposite polarity across the electrodes while a first image is projected onto the first electrode, thereby switching the ferroelectric remanent polarization of said ferroelectric material in areas corresponding to said first image which results in the storage of said first image in the ferroelectric material, means to project a second image in the near ultraviolet or visible region of the spectrum onto the first electrode thereby to generate charge carriers on the first electrode in the areas which were illuminated, and means to measure a short-circuit photocurrent across the first and second electrodes, thereby to determine the two-dimensional dot product of the stored and projected images and the degree of correspondence between the first and second images. 
     
     
       2. The device of claim 1, wherein the ferroelectric material is lead lanthanum zirconate titanate. 
     
     
       3. The device of claim 2, wherein a ferroelectric solid solution is used having the formula:   Pb.sub.l-x La.sub.x (Zr.sub.y Ti.sub.z).sub.l-x/4 O.sub.3     where y+z=1.   
     
     
       4. The device of claim 1, wherein the ferroelectric material is from about 0.2 μm to 10 μm in thickness. 
     
     
       5. The device of claim 1, wherein the first electrode is aluminum. 
     
     
       6. The device of claim 5, wherein the aluminum is sputtered onto the ferroelectric thin film. 
     
     
       7. The device of claim 5, wherein the aluminum is deposited onto the ferroelectric thin film by vapor deposition. 
     
     
       8. The device of claim 1, wherein the first electrode is gold. 
     
     
       9. The device of claim 1, wherein the first electrode is indium-tin oxide. 
     
     
       10. The device of claim 1, wherein the second electrode is platinum. 
     
     
       11. The device of claim 10, wherein the second electrode is 0.5 μm thick. 
     
     
       12. The device of claim 1, wherein the ferroelectric material is about 1 μm thick. 
     
     
       13. The device of claim 1, further comprising a non-conductive substrate attached to the outer surface of the second electrode. 
     
     
       14. The device of claim 13, wherein said substrate is silicon 
     
     
       15. A ferroelectric thin-film device for image comparison, comprising: (a) a thin-film polycrystalline ferroelectric material having a first and second surface, a substantial portion of said first surface being in contact with a semi-transparent or transparent first electrode material and a substantial portion of said second surface being in contact with a second electrode;   (b) means to apply a first voltage bias to said first electrode with respect to said second electrode;   (c) means to apply a second voltage bias to said first electrode;   (d) means to simultaneous project a first image on said thin-film polycrystalline ferroelectric material while said second voltage bias is applied thereby to store said first image;   (e) means to project a second image onto said polycrystalline ferroelectric material thereby generating a short circuit photocurrent between said first and second electrodes;   (f) means to measure said short circuit photocurrent representative of a product of polarization and illumination intensity which is further represented by a dot product to thereby compare said first and second images.   
     
     
       16. The device of claim 15, wherein the first electrode is aluminum. 
     
     
       17. The device of claim 15, wherein the first electrode is indium tin oxide. 
     
     
       18. The device of claim 15, wherein the ferroelectric material is lead lanthanum zirconate titanate. 
     
     
       19. The device of claim 8, wherein the ferroelectric material is lead lanthanum zirconate titanate. 
     
     
       20. A ferroelectric thin-film device, as in claim 15, wherein said thin-film polycrystalline ferroelectric material is a film of ferroelectric lead lanthanum zirconate titanate about 0.2 to 10 μm thick having a first and second surface, said first surface being in contact with a layer of aluminum semi-transparent to near UV or blue radiation as said first electrode material, and said second surface being in contact with a platinum electrode as said second electrode for use in an image comparator. 
     
     
       21. A ferroelectric thin-film device for comprising a thin-film polycrystalline ferroelectric material having a first and second surface, a substantial portion of said first surface being in contact with a semi-transparent or transparent first electrode material and a substantial portion of said second surface being contact with a second electrode, in combination with an ammeter connected to measure the short-circuit current between the first and second electrodes, a translation drive means connected to the thin-film device to move it relative to an image projected onto its surface, and a microprocessor connected to the ammeter and translation device to direct the movement of the thin-film device in a predetermined pattern to form an image correlation device.